The overall objective of this project is to contribute to an understanding of the integrated processes by which the plasma membrane and associated external and internal surfaces control and regulate the behavior of the cells during development and aging, both in vivo and in vitro. Research goals for the current year (-06; 1980-81) will be 1) completion of studies of the distribution, quantitation and internalization of lectin binding to external surfaces of aging cell populations using scanning optical densitometry, fluorescence microscopy and techniques of electron microscopy; 2) completion of the structural characterization of cycle dependent features of membrane organization in age-related culture groups using freeze-fracturing and electron microscopy; 3) completion of studies of surface-mediated control of cellular proliferation through cyclic nucleotides using fluorescence-activated cell sorting, flow microfluorometry and radioimmunoassay; and 4) continuation of studies using automated cell sorting to characterize subpopulations of cells in progressively subcultivated IMR-90 cells.